The present invention relates to a method for determining the point to start the rounding phase when turning veneer from a log. The rounding phase is the initial point of veneer turning, wherein irregularities are removed and the log is rounded for the actual veneer cutting, in other words, the initial phase of turning during which the peeling knife does not yet meet the entire surface of the log, whereby the veneer sheet thus turned is fall of splits.
A preliminary phase in veneer turning is the centering of the log, wherein the optimum positions at the log ends for the insertion of the lathe spindles are defined based on the diameter and shape of the log so that the log when turned about the spindle insertion points gives a maximum yield of veneer. In this centering phase, also the maximum diameter of the log is determined and the thus obtained information is used in setting the knife carriage in the initial phase of turning.
When a new log to be turned is being mounted on the lathe, the knife carriage is withdrawn into the rear starting position of the radial feed movement, that is, into a home position, wherein the knife will at all times permit free rotation of the log mounted on the spindles. When the turning phase starts, the knife carriage is driven at a fast rate in the cutting direction into a position determined from the log maximum diameter information obtained from the centering phase. From this position onward, the knife carriage is driven forward at a feed rate defined for the log rounding phase until the log is rounded.
This procedure has been problematic in conjunction with bumpy logs that may have a stub of a thick branch, for instance. However, conventional centering methods and apparatuses are incapable of coping with such projecting bumps, whereupon the set value of knife feed rounds the log at the bump at a fast-feed rate. As a result, the apparatus is subjected to excessive stresses and the log will split due to the unduly fast knife feed rate.
These problems can be rectified by virtue of the method according to the invention, wherein the starting point of log rounding turning is determined, as is characteristic to the invention, by monitoring the intensity of the knife carriage vibration during the initial turning phase occurring at a fast feed rate and then using the thus obtained intensity value of the knife carriage vibration for the determination of the initial position of the log rounding phase.
It is known in the art to measure the intensity value of knife carriage vibration, whereby the thus obtained measurement result is used for controlling the inclination of the knife carriage relative to the log being turned. Such an embodiment is described, e.g., in FI Pat. No. 94,608. Obviously, an equivalent equipment is also applicable in the implementation of the present invention.